Reason:
Not only CON but also we cant create a folder with many words like PRN, AUX, CLOCK$, NUL , COM1, COM2, COM3, COM4, COM5,COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9 .
This are reserved keywords used by DOS.
These folders are already existing folders so when you try to create these folders then windows gets confused because of ambiguity.